An elegant strategy for proving impossibility results
in distributed computing was introduced in
the celebrated FLP consensus impossibility proof [1]}.
This strategy is local in nature as at each stage,
one configuration of a hypothetical protocol for consensus is considered,
together with its future valencies, namely,
the decisions the protocol may reach from this configuration.
To apply it, one needs to consider only the interactions of pending
transitions at the configuration,
and analyze their commutativity properties.
This local nature makes the strategy very powerful and flexible, and has therefore
been used in numerous situations related
to consensus (e.g., [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}).
